Wind-Induced Barotropic Motions in Long Lakes

Abstract

Water motion in the barotropic mode, directly forced by suddenly imposed wind stress, is investigated in basins with arbitrary topography, but paying special attention to long basins, in which the depth contours run parallel to the shores over a ?trunk? region. In the initial period the depth-integrated transport is found to increase linearly in time; later, friction slows down this increase. Where the water is shallower than the average depth of the lake, transport is with the wind; it is against the wind in the deeper portion. Over the entire basin, a transport-streamline pattern may be calculated numerically, which is identical in appearance with the steady-state flow pattern calculated on the basis of assuming bottom friction to be linearly related to transport. A more realistic frictional force (quadratic in the velocity) modifies this pattern somewhat, but does not change it qualitatively. An analysis of IFYGL coastal chain observations in Lake Ontario shows that the observed nearshore transport behaves much as the theoretically derived forced flow pattern. One may conclude that in nearshore areas (for practical purposes, in water shallower than the basin average depth), the forced component of the flow dominates the observable depth-integrated transport, oscillating movements (seiches) being relatively less important. This forced flow pattern may be described as consisting of barotropic coastal jets.